High intensity lights are needed for beacons for navigation and obstruction avoidance. For example, obstruction beacons must be capable of meeting the 20,000 cd requirements for the FAA (US Federal Aviation Authority) L865-L864 standard and the ICAO (International Civil Aviation Organization) Medium Intensity Navigation Lights. In the past, lamps have used conventional strobe lights. However, such lights are energy and maintenance intensive. Recently, lamps have been fabricated using light emitting diodes (LEDs). LEDs create unique requirements in order to be commercially viable in terms of size, weight, price, and cost of ownership compared to conventional strobe lights.
In the example of 20,000 cd beacons, the FAA and ICAO regulations set the following stringent requirements for beam characteristics at all angles of rotation (azimuth). Lights must have effective (time-averaged) intensity greater than 7500 candela (cd) over a 3° range relative to the horizon (elevation). Lights must also have peak effective intensity of 15,000-25,000 cd and effective intensity window at −1° elevation of “50% min and 75% max” for the ICAO only. The ICAO standard sets this “window” of beam characteristics at −1° of elevation and must be met at all angles of rotation (azimuth).
Light devices must also meet the requirements of the FAA compliant version producing 60,000 cd peak intensity in 100 msec flashes. Such lights must also meet the requirements of the ICAO compliant version producing 25,333 cd peak intensity in 750 msec flashes. Ideally, lights can also be combined or configured to provide 2,000 cd red light in addition to the 20,000 cd white light for day and night time operation.
In order to achieve the total light intensity required for an FAA or ICAO compliant light using LEDs, it is necessary to use a large number of LED light sources. However, it is difficult to create a beam with the desired intensity pattern when directing large numbers of LED sources into few reflectors. Furthermore, smaller and therefore more numerous reflectors are needed to conform to overall size restrictions. These constraints all result in a design with a large number of optical elements comprised of individual LEDs and small reflectors. A final challenge is alignment of the multiple optical elements such that their outputs combine to form a beam that is uniform at all angles of azimuth.
Currently, available LED lamps typically stack multiple optical elements symmetrically with no offset, as well as use large reflectors and multiple LEDs per reflector. While such lamps may be compliant, they typically require more than optimal number of LEDs and thus are more complex and expensive.
Thus an efficient LED-based lamp that consistently and readily meets FAA and ICAO standards currently does not exist. An LED lamp that allows the use of relatively smaller reflectors is desirable to meet such standards.